1. Field of the Invention
This invention relates to door assemblies in which a door is hinged to a frame along a non-vertical hinge line and torque rods are used to counterbalance the door so that it can easily be lifted against the force of gravity. The invention particularly relates to large, heavy load-bearing doors such as flush-mounted sidewalk or floor access doors where it is desirable to precast the door and frame into a concrete slab.
2. Description of Related Art
There are numerous applications in which a door is hinged along a non-vertical hinge line and must be opened and closed against the force of gravity. Such applications include sidewalk access doors, floor hatches, roof hatches, elevator and machinery access panels and the like. Such doors are often used in areas where foot traffic is expected, or where vehicle traffic may occur, and therefore must be extremely strong and are usually quite heavy.
Doors of this type can be dangerous due to their tendency to close rapidly and with great force when released, and it has been common to provide some means of counterbalancing to eliminate this danger. An additional benefit obtained by counterbalancing is that the door can be opened more easily by individuals with less risk of back strain, or can be motorized and opened with less power and with smaller motors.
In doors of this type, the counterbalancing has usually been provided by tubular compression spring operators. Where the doors are particularly heavy, multiple compression spring operators have been used.
Multiple compression spring operators have been preferred for heavy applications because of the force which can be generated and the simplicity with which they can be ganged together to provide the necessary counterbalancing. However, to achieve the necessary counterbalancing force over the required distance, compression springs must extend significantly below the level of the door and frame. A typical spring length has been twelve (12) inches (30 centimeters), while door frames are usually only 3-4 inches (8-10 centimeters) high and concrete slabs are usually only 6 inches (15 centimeters) thick.
Thus, compression springs have disadvantages in certain applications, particularly where the door is to be precast into a concrete slab, or where the space below the door will be used as a work space and the headroom is limited. In precasting operations where the standard slab is six (6) inches (15 centimeters) thick, the compression springs do not fit into the precaster's molds and holes must be cut into the mold to accommodate the length of the spring.
For lighter doors, torque rods have occasionally been used in the counterbalancing mechanism. However, there is a problem in that torque rods provide a counterbalancing torque which is a linear function of their twist, while a non-vertically hinged door requires a counterbalancing torque which is a sinusoidal function of the opening angle.
Nonetheless, previous torque rod counterbalancing systems were designed to directly twist the rod by the same amount as the opening angle of the door by connecting one end of the rod to the door and one end to the frame. This was a convenient way to twist the rod and apply some counterbalancing torque, but it resulted in only partial counterbalancing. Usually the door was undercompensated at the center of its range which made the torque rod system poorly suited for counterbalancing heavy doors where the amount of uncompensated weight was high.
Bearing in mind these and other deficiencies of the prior art, it is therefore an object of the present invention to provide a counterbalanced door and frame assembly suitable for use with large, heavy non-vertically hinged doors in which the door is substantially counterbalanced by torque rods over its entire opening range.
An additional object of the invention is to provide a means of coupling multiple torque rods to increase the torque available and counterbalance heavier doors.
Another object of the invention is to provide a simple yet strong method for engaging the rods to be twisted and for shaping the rods with bent ends such that different left and right-hand versions of the rods are not required.
A further object of the invention is to provide a counterbalanced door and frame assembly wherein the frame forms a continuous wall around the door and wherein the counterbalance mechanism does not project below the level of the frame such that the assembly is suitable for precasting into a concrete slab.
Still another object of the invention is to provide a torque rod arm and cam counterbalancing mechanism wherein the cam is provided with a track for guiding and stabilizing the torque rod arm under heavy counterbalancing loads.